The reason this happens is that people are charged for throwing away certain kinds of rubbish in Japan. Electrical appliances are expecially expensive to throw out. For example, a person I know was charged 8000 yen (approx US$80) for throwing out an old microwave, TV, and stereo speakers.
So instead of having the rubbish collected and disposed of properly by the city government, many people dump stuff illegaly to avoid the disposal fees.